Manhood Peninsula SurfaceSurface WaterWater ManagementManagement PlanPlan (SWMP)(SWMP) Non Technical Summary

What is a SWMP? The SWMP Surface Water Management Plans, or SWMPs for short, The SWMP for the Manhood Peninsula has been look at flooding that occurs in response rainfall when: prepared by CH2M HILL on behalf of West  Sewers and drains become inundated Council. Work began in July 2014 and the final report was issued in August 2015.  Waterlogged ground leads to runoff from land  Small rivers and/or ditches overflow The study area is shown in Figure 1 below. The A27  Water contained within rocks under the ground forms the northern boundary of the study area while the rises up above the surface (this is called Pagham Rife forms the eastern boundary. To the west groundwater flooding). the study boundary is determined by Harbour. Drainage in the Manhood Peninsula discharges A SWMP sets out a long-term action plan for dealing either to , Pagham Harbour or direct with types of flooding. to the sea.

Figure 1 – Manhood Peninsula SWMP Study Area

Manhood Peninsula – Non Technical Summary

Manhood Peninsula Surface Water Management Plan (SWMP)

Throughout the development of the SMWP there has data, and information on historic rainfall, topography and been close engagement with key stakeholders, including drainage. All this information was compiled and mapped County Council (WSCC), Chichester using computer based Geographic Information Systems. District Council, The Environment Agency, Southern Water, parish councils and local flood action groups, Manhood Peninsula Partnership and Manhood Wildlife and Heritage Group (MHWG). Objectives The objectives of the Manhood Peninsula SWMP were to:  understand the surface water drainage in this area and gather additional data to reduce gaps in knowledge;  identify pinch points in the network and connectivity issues;  identify potential improvement works to reduce flood risk to communities in the Peninsula including capital and maintenance measures, building on the work already undertaken by communities, Flooding in North (June 2012) partnerships and other organisations;  produce up to date GIS data of the ditch network, building on the work undertaken by Royal Recent flooding issues Haskoning, based on site visits undertaken to various locations in the Peninsula The Manhood Peninsula has suffered from river and coastal flooding, such as overtopping of the coastal Methodology defences to the west of in 2005. Furthermore, during extreme rainfall events or very wet winters The methodology for the project broadly follows the significant flooding occurs across the Manhood SWMP Technical Guidance published by DEFRA in Peninsula, as was the case in autumn 2000, June 2012, 2010. The key project stages were as follows: Winter 2012/13 and Winter 2013/14. During these extreme rainfall events or wet winters flooding occurs from Rifes, local ditch networks and the highway • Data collection and review drainage system as they do not have sufficient capacity 1 • Define the study area to drain water away. In addition to flooding during more extreme rainfall • Analyse the data events or wet winters, the Manhood Peninsula is • Identify flooding hot spots vulnerable to regular flooding due to its low-lying nature. 2 This regular flooding is often caused by poor maintenance of ditches and culverts, discontinuity of the • Consult with stakeholders ditch network, or collapses/blockages in piped ditches or 3 • Undertake site visits with stakeholders drainage. Flooding of this nature can emerge anywhere if ditches are blocked or there are collapses/blockages in the piped drainage network.

• Consider options to alleviate flooding The most detailed evidence of flooding across the 4 Manhood Peninsula is available from WSCC highway incident logs from June 2012 to March 2014. As the time period covers a major summer storm event (June 2012), and two extremely wet winters (2012/13 and 2013/14) it Data is reasonable to assume that the incident logs provide a A wide range of data was collated and analysed to help good representation of the flooding impacts across the understand the local flooding issues. This included data Manhood Peninsula. The areas which experienced the from previous studies of the Manhood Peninsula (e.g. highest number of properties (>5) affected by flooding Royal Haskoning Land Drainage Study), historic flooding during this period included:

Manhood Peninsula SWMP – Non Technical Summary

Manhood Peninsula Surface Water Management Plan (SWMP)

 Almodington; Moderate  Crouchers (A286)  ; priority  ;  ;  Stockbridge  Hunston;   Selsey;

;  Somerley, and; Potential measures  . In addition, a number of key transport routes are In the past few years there has been a concerted effort vulnerable to flooding (e.g. A286), which affects the by WSCC, parish councils, local flood action groups, the movements of people across the Manhood Peninsula. Environment Agency, and the MWHG to manage drainage and flooding across the Manhood Peninsula. Identifying the communities most This has made a significant improvement to the management of flooding. Further maintenance mitigation vulnerable to flooding measures are needed to reduce flooding and ensure the To identify the priority locations for the SWMP the ‘key drainage infrastructure is functioning as intended. areas for drainage’ identified in Phase 3 of the Royal Haskoning Land Drainage Study were considered. There were 48 key areas for drainage identified by Royal Haskoning. Subsequently, in each of these areas it was identified whether there had been flooding to property and infrastructure based on the WSCC highway incident logs, Southern Water’s sewer flooding register, and information gathered from the stakeholder meetings. Areas where no flooding was recorded were excluded from further analysis. In addition, during this stage any additional areas which suffered flooding which had not been identified as key areas for drainage were considered. Following this process there were 21 locations short- listed for further consideration. The remaining 21 locations were prioritised into the highest, moderate, or Florence Pond, Sidlesham low/other priority areas, based on: However, in a low-lying area such as the Manhood  the number of properties at risk or flooded Peninsula the drainage system is highly sensitive to internally; blockages and poor maintenance which will hinder the  the type of road affected by flooding; flow of flood water. Therefore the drainage system  the underlying cause of flooding, and; needs to be maintained on a cyclical basis rather than  whether action had already been taken to reduce relying solely on one off improvements. There is a risk flooding in a community. that without ongoing maintenance and management the Using this approach identified seven high priority works undertaken over the past few years will prove locations, five moderate priority locations and nine lower ineffective in (say) five years’ time and flooding will re- priority locations (which were not considered in further occur. detail in the SWMP). These locations are listed in the This is because without ongoing maintenance and table below. management ditches will not be maintained, culverts and High priority  Birdham & Westlands piped drainage will become blocked, and householders will continue to infill ditches without thought to flooding  East Wittering & Bracklesham issues. In addition, the current approach tends to be  Hunston reactive to flooding problems as they emerge. A  Selsey proactive approach would reduce the risk of flooding  Sidlesham before it began.  Somerley  West Wittering The SWMP has therefore identified a strategy to manage flooding in the short-term (0-2 years) and

Manhood Peninsula SWMP – Non Technical Summary

Manhood Peninsula Surface Water Management Plan (SWMP)

considers ongoing measures to reduce flooding to The ongoing management and investment should be people, property and roads in the Manhood Peninsula based around four key themes: over the next 10 years. Short-term action plans were  importance of land drainage consents developed for each of the 12 high and moderate priority the to locations. These action plans set out the measures prevent culverting or infilling of watercourses where required in the short-term and who is responsible for it will increase flood risk;  need to control runoff from new progressing each action. The action plans also consider the developments the potential impact of measures on downstream flood ; risk, and the environmental considerations which should  the requirement to continue maintaining be taken into account when implementing the actions. watercourses, culverts and highway drainage on The action plans are contained in Section 5 of the main a cyclical basis, and; report.  the need to control runoff from glass houses in the Manhood Peninsula. In the longer term ongoing management and maintenance will be critical to manage flooding. The The objective is to ensure that the drainage system is SWMP identified five principles which are considered the managed and maintained on a proactive, cyclical basis fundamental elements to ensuring continued long term to ensure it is functioning as intended. This can be maintenance and management of the drainage system achieved through an annual walkover survey of the across the Manhood Peninsula: critical drainage routes to identify their condition, maintenance requirements and any land drainage  ditch clearance remains the responsibility of riparian consent issues. This should take place in late autumn to owners and landowners; allow vegetation die back following the summer, but also  local communities have a key role to play; to identify any remedial measures before the wet winter  runoff into the ditch network needs to be controlled; months when the Manhood Peninsula is primarily  the continuity of the ditch network is critical, and; affected by flooding  a consequence-based approach should be adopted (i.e. focusses on the critical parts of the drainage network).

Figure 2 – Manhood Peninsula Drainage Flooding Strategy

Manhood Peninsula SWMP – Non Technical Summary